Methods and apparatus for processing and dispensing material during additive manufacturing

ABSTRACT

A system for additive manufacturing includes a nozzle configured to translate along a first axis, a second axis perpendicular to the first axis, and a third axis orthogonal to the first and second axes, wherein the nozzle is operably coupled to: an extruder having an outlet and including a screw disposed within a barrel, and a pump having an inlet and an outlet. The inlet is coupled to the extruder, and the outlet is in fluid communication with the nozzle. The system also includes a controller configured to adjust a speed of the pump with respect to a speed of the screw to apply a target pressure at the outlet of the extruder.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation-in-part of pending U.S. patentapplication Ser. No. 15/253,290, filed Aug. 31, 2016, the entirety ofwhich is incorporated by reference herein.

TECHNICAL FIELD

Aspects of the present disclosure relate to apparatus and methods forfabricating components. In some instances, aspects of the presentdisclosure relate to apparatus and methods for fabricating components(such as, e.g., automobile parts, medical devices, machine components,consumer products, etc.) via additive manufacturing techniques orprocesses, such as, e.g., 3D printing manufacturing techniques orprocesses.

BACKGROUND

Additive manufacturing techniques and processes generally involve thebuildup of one or more materials to make a net or near net shape (NNS)object, in contrast to subtractive manufacturing methods. Though“additive manufacturing” is an industry standard term (ASTM F2792),additive manufacturing encompasses various manufacturing and prototypingtechniques known under a variety of names, including freeformfabrication, 3D printing, rapid prototyping/tooling, etc. Additivemanufacturing techniques are capable of fabricating complex componentsfrom a wide variety of materials. Generally, a freestanding object canbe fabricated from a computer-aided design (CAD) model.

A particular type of additive manufacturing is more commonly known as 3Dprinting. One such process commonly referred to as Fused DepositionModeling (FDM) comprises a process of melting a very thin layer of aflowable material (e.g., a thermoplastic material), and applying thismaterial in layers to produce a final part. This is commonlyaccomplished by passing a continuous thin filament of thermoplasticmaterial through a heated nozzle, which melts the thermoplastic materialand applies it to the structure being printed. The heated material isapplied to the existing structure in thin layers, melting and fusingwith the existing material to produce a solid finished product.

The filament used in the aforementioned process is generally producedusing an extruder. In some instances, the extruder may include aspecially designed screw rotating inside of a barrel. The barrel may beheated. Thermoplastic material in the form of small pellets isintroduced into one end of the rotating screw. Friction from therotating screw, combined with heat from the barrel softens the plastic,which then is forced under pressure through a small opening in a dieattached to the front of the extruder barrel. This extrudes a string ofmaterial which is cooled and coiled up for use in the 3D printer as theaforementioned filament of thermoplastic material.

Melting a thin filament of material in order to 3D print an item is aslow process, which is generally only suitable for producing relativelysmall items or limited number of items. As a result, the melted filamentapproach to 3D printing is too slow for the manufacture of large itemsor larger number of items. However, 3D printing using moltenthermoplastic materials offers many benefits for the manufacture oflarge items or large numbers of items.

A common method of additive manufacturing, or 3D printing, generallyincludes forming and extruding a bead of flowable material (e.g., moltenthermoplastic), applying the bead of material in a strata of layers toform a facsimile of an article, and machining such facsimile to producean end product. Such a process is generally achieved by means of anextruder mounted on a computer numeric controlled (CNC) machine withcontrolled motion along at least the X, Y, and Z-axes. In some cases,the flowable material, such as, e.g., molten thermoplastic material, maybe infused with a reinforcing material (e.g., strands of fiber) toenhance the material's strength. The flowable material, while generallyhot and pliable, may be deposited upon a substrate (e.g., a mold),pressed down or otherwise flattened to some extent, and leveled to aconsistent thickness, preferably by means of a tangentially compensatedroller mechanism. The flattening process may aid in fusing a new layerof the flowable material to the previously deposited layer of theflowable material. In some instances, an oscillating plate may be usedto flatten the bead of flowable material to a desired thickness, thuseffecting fusion to the previously deposited layer of flowable material.The deposition process may be repeated so that each successive layer offlowable material is deposited upon an existing layer to build up andmanufacture a desired component structure. When executed properly, thenew layer of flowable material may be deposited at a temperaturesufficient enough to allow a new layer of such material to melt and fusewith a previously deposited layer, thus producing a solid part.

In the practice of the aforementioned process, a major disadvantage hasbeen encountered. Material extruders, of the type used in near net shape3D printing, are designed to operate at a constant steady rate in orderto produce a steady, consistent homogeneously melted plastic bead. Inmost cases, however, the majority of heat energy required to melt theplastic is generated by friction from a screw turning inside a barrel.This steady extrusion rate, however, creates difficulties when 3Dprinting. Specifically, the computer numeric controlled (CNC) machineused to move the extruder-based print head cannot start and stopinstantaneously, and must, by necessity, vary in speed as it traces thepath required to print the part.

This combination of a machine moving at variable speeds and an extrusionhead outputting material at a constant rate results in a print bead thatcould vary in size. That is, the bead is thicker when the machine headis moving slowly, and thinner when the machine operates at a relativelyhigher speed.

A common approach employed in addressing the aforementioned problem isto servo-control the extrusion screw, speeding it up when the machine ismoving faster and slowing it down as the machine motion slows. Sincemuch of the energy used to melt the plastic is generated by rotation ofthe screw in the barrel of the extruder, varying the speed not onlyvaries the rate by which material is pumped through the extruder but italso varies the amount of heat energy generated for melting the flowablematerial, such as, e.g., thermoplastic. The consequential increasedtemperature results in the thermoplastic material being less viscous;and, therefore, flowing faster than when it is cooler and thereby moreviscous. The effect is that the flow rate from the extruder at any pointin time is determined not only by the rotational speed of the extrusionscrew, but also by the recent history of rotation, which determines howhot and thus how viscous the melted material is. This means that in asystem where the rotation speed of an extruder varies randomly withtime, the amount of material flowing from an extruder at a specificrotation speed will not be at a constant rate. Therefore, if theextruder screw is servo-controlled to operate at a specific rotationalspeed for a specific velocity of the print head, the resulting printedbead will not be consistent. Thus, method and apparatus are needed toproduce a consistent print bead size when 3D printing.

Furthermore, the extruder may function to take polymer material inpellet form, heat, soften, and mix the material into a homogenized melt,and then pump the melt under pressure into a die to form the materialinto a useful extruded shape. This may be accomplished by providing anauger-type screw rotating inside a heated barrel, for example. Thegeometry, clearances, composition, and functionality of the screw and abarrel of the extruder may be determined as necessary to provide anextruder that operates as desired.

The extruder may be provided with the goal of completely mixing themelted material (e.g., polymer material) into a smooth, consistent formwith no unmelted pellet portions or temperature variations in the meltedmaterial. One method of achieving this objective includes installing abreaker plate at the exit end of the extruder. A breaker plate may be,for example, a disk or plate that has a series of holes that provideresistance to the flow of the polymer melt. The holes in the breakerplate may be uniform holes approximately 0.125″ inches in diameter, andmay be machined through the entire thickness of the breaker plate so asto be aligned with the flow direction of the polymer melt. This breakerplate may restrict the flow of material, increasing pressure inside theextruder barrel which assists in the melting and mixing process. One ormore mesh screens or filters may be installed before the breaker plateto further restrict flow and increase pressure to aid mixing.

There may an optimal pressure range within which a particular extruderoperates most effectively. Generally, a breaker plate and one or moremesh screens are installed in an effort to generate and maintain thisdesired pressure during operation of the extruder. While the inclusionof a breaker plate and/or screen may improve some mixingcharacteristics, they may also introduce drawbacks. For example, theadditional restriction to flow may reduce throughput. Additionally,different polymers may require different breaker plate and/or screenconfigurations to achieve a desired pressure. Thus, the breaker plateand/or screen may need to changed each time the polymer being extrudedchanges in order to achieve a desired pressure that corresponds to theextruded polymer.

Another approach to achieve enhanced mixing may be to include knobs orother shapes on the extrusion screw, creating a “mixing section” whichagitates the melt. This approach may also reduce flow of the melt and,in some cases, the friction caused by the mechanical mixing action cancreate unwanted heat in the mixing section.

Another purpose of the screen and/or breaker plate may be to create agenerally fixed amount of resistance to the material flow in theextruder. This may facilitate generating and maintaining a steady statemelt process within the extruder. If the breaker plate and/or screenwere not in place in a typical extruder configuration, the amount ofresistance to melt flow, and thus the operating pressure inside theextruder may depend solely or nearly primarily on the amount ofresistance created by the shape of the forming die through which themelt flows after exiting the extruder. It may then become difficult toachieve consistent operation since the extruder may process materialthrough a variety of different die shapes, each with a differentresistance to flow. Some dies may generate insufficient resistance toflow to achieve optimal operating pressure while others may generatesignificantly higher pressure than is desired.

SUMMARY

Aspects of the present disclosure relate to, among other things, methodsand apparatus for fabricating components via additive manufacturing,such as, e.g., 3D printing techniques. Each of the aspects disclosedherein may include one or more of the features described in connectionwith any of the other disclosed aspects.

In one aspect, a system for additive manufacturing may include a nozzleconfigured to translate along a first axis, a second axis perpendicularto the first axis, and a third axis orthogonal to the first and secondaxes, wherein the nozzle may be operably coupled to: an extruder havingan outlet and including a screw disposed within a barrel, and a pumphaving an inlet and an outlet. The inlet may be coupled to the extruder,and the outlet may be in fluid communication with the nozzle. The systemmay also include a controller configured to adjust a speed of the pumpwith respect to a speed of the screw to apply a target pressure at theoutlet of the extruder.

In another aspect, a system for additive manufacturing may include anozzle configured to translate along a first axis, a second axisperpendicular to the first axis, and a third axis orthogonal to thefirst and second axes. The nozzle may be operably coupled to: anextruder including a screw disposed within a barrel, and a pump havingan inlet and an outlet wherein the inlet may be coupled to the extruder,and the outlet may be in fluid communication with the nozzle. The systemmay include a controller configured to modify a size of a bead extrudedby the nozzle to maintain an approximately constant sized overlapbetween a plurality of adjacent beads.

In another aspect, an additive manufacturing method for delivering aflowable material from a nozzle of a programmable computer numericcontrol machine (CNC) may include actuating an extruder to form aflowable material, delivering the flowable material to a pump, andoperating the pump at a speed. The method may also include adjusting atleast one of the speed of the pump or a rate of translation of thenozzle based on a size of a boundary area formed by at least oneadjacent bead of flowable material.

As used herein, the terms “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus. The term “exemplary” isused in the sense of “example,” rather than “ideal.”

It may be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the disclosure, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate exemplary aspects of the presentdisclosure and together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is a perspective view of an exemplary CNC machine operablepursuant to an additive manufacturing process in the formation articles,according to an aspect of the present disclosure;

FIG. 1A is a perspective view of an exemplary CNC machine operablepursuant to an additive manufacturing process in the formation articles,according to another aspect of the present disclosure;

FIG. 2 is an enlarged perspective view of an exemplary carriage andapplicator assembly of the exemplary CNC machine shown in FIG. 1;

FIG. 2A is an enlarged perspective view of an exemplary carriage andapplicator head of the exemplary CNC machine shown in FIG. 1A;

FIG. 3 is an enlarged cross-sectional view of an exemplary applicatorhead assembly of the exemplary carriage assembly of FIG. 2;

FIG. 3A is an enlarged cross-sectional view of an exemplary applicatorhead of FIG. 2A;

FIG. 4 is a cross-sectional view of a schematic representation of themajor mechanical components of an extruder assembly of the presentdisclosure, along with an exemplary flow diagram of the associated servosignals;

FIG. 4A is a cross-sectional view of a schematic representation of themajor mechanical components of an extruder assembly of the exemplary CNCmachine shown in FIG. 1A, along with an exemplary flow diagram of theassociated servo signals;

FIG. 5 is an enlarged perspective view illustrating beads of flowablematerial that may be deposited by the exemplary applicator head assemblyof the exemplary CNC machines shown in FIGS. 1 and 1A;

FIG. 6 is a top partially-schematic view showing beads of flowablematerial that may be deposited by the exemplary applicator head assemblyof the exemplary CNC machines shown in FIGS. 1 and 1A;

FIG. 7 is cross-sectional view showing beads of flowable material and avoid that may be filled by the exemplary applicator head of theexemplary CNC machines shown in FIGS. 1 and 1A; and

FIG. 8 is a cross-sectional view showing the void of FIG. 7 after thevoid has been filled with a bead of flowable material that may bedeposited by the exemplary applicator head of the exemplary CNC machinesshown in FIGS. 1 and 1A.

DETAILED DESCRIPTION

The present disclosure is drawn to, among other things, methods andapparatus for fabricating multiple components via additive manufacturingtechniques, such as, e.g., 3D printing. More particularly, the methodsand apparatus described herein comprise a method for eliminating, orotherwise substantially minimizing variations in the flow-rate of amolten flowable material (e.g., a thermoplastic material) in an additivemanufacturing process, by, e.g., providing a servo-controlledfixed-displacement pump (e.g., polymer pump) between the output of anextruder and an application nozzle of a CNC additive manufacturingmachine. For purposes of brevity, the methods and apparatus describedherein will be discussed in connection with fabricating parts fromthermoplastic materials. However, those of ordinary skill in the artwill readily recognize that the disclosed apparatus and methods may beused with any flowable material suitable for additive manufacturing,such as, e.g., 3D printing.

In one aspect, the present disclosure is directed to an extruder-based3D printing head that can deposit melted material (e.g., thermoplasticmaterial) when the print head is traveling at a high rate of speed. Inanother aspect, the present disclosure is directed to depositingmaterial at a consistent controlled rate at any time regardless of melttemperature variations caused by the history of changes in rotationalspeed of a screw of the extruder.

In certain sectors of the plastics industry, there are applications inwhich polymer pumps (also referred to herein as a gear pump) aresometimes utilized, in conjunction with plastic extruders. A polymerpump is a fixed displacement gear pump, which meters a fixed amount ofmaterial with each rotation of the pump. Polymer pumps are typicallyused in operations such as the co-extrusion of two or more materials,where synchronization of the flow rates is critical.

In order for a polymer pump to function properly, the plastic extrudermust supply melted material to the input of the polymer pump at arelatively fixed input pressure. The aforementioned method ofcontrolling the rotation of the extruder screw by means of a servo loop(e.g., speeding up the rotation when the pressure drops, or is too low,and slowing down the rotation when the pressure is high) works well in abasic extrusion application because input pressure variations in such asituation are generally slight. As a result, only minor changes to therotational speed of the extruder screw are necessary to ensure thepolymer pump receives melted material at a relatively constant inputpressure.

In 3D printing, however, the addition a polymer pump alone to regulateflow-rate does not work satisfactorily. The 3D printing process bynature requires frequent variations in the speed of the print head dueto a number of factors. For example, one factor may include speedchanges, which are required when applying material in tight arcs orthrough corners. Speed changes may be necessary when a change indirection of travel for the print head is required. Even with theaddition of a polymer pump, variations in the flow rate of such a pumpcan be dramatic, resulting in servo demands for rapid and substantialchanges in extruder rotation speed. A rapid change in extruder screwrotation speed does not immediately translate into a rapid change inflow rate of the melted flowable material. There is a substantial delaybetween a change in extruder screw speed and a resulting change in flowrate of the melted material. This delay makes the traditional steadystate servo approach unworkable when operating with a polymer pump thatvaries in output rate. For example, if the extruder accelerates quickly,as material is advanced within, the input pressure to the polymer pumpwill drop, resulting in the servo system quickly increasing the speed ofthe extruder screw. A delay in the drop in input pressure until aftermaterial is moving in the polymer pump, combined with a delay inincreased flow rate from the extruder, may allow the input pressure todrop low enough to interrupt a proper flow of material, which results ina deposited bead of inconsistent size and shape.

To address the aforementioned problem, the present disclosure utilizes amodified servo signal approach. Using special algorithms, the controlsystem coordinates the extruder speed with the speed of the polymer pump(gear pump) so that speed increases and/or decreases in both units atthe same time. In addition to being simultaneous, the speed changes maybe proportional.

With reference now to FIG. 1 of the drawings, there is illustrated aprogrammable computer numeric control (CNC) machine 1 embodying aspectsof the present disclosure. A controller (not shown) may be operativelyconnected to machine 1 for displacing an application nozzle along alongitudinal line of travel or x-axis, a transverse line of travel or ay-axis, and a vertical line of travel or z-axis, in accordance with aprogram inputted or loaded into the controller for performing anadditive manufacturing process to replicate a desired component. CNCmachine 1 may be configured to print or otherwise build 3D parts fromdigital representations of the 3D parts (e.g., AMF and STL format files)programmed into the controller. For example, in an extrusion-basedadditive manufacturing system, a 3D part may be printed from a digitalrepresentation of the 3D part in a layer-by-layer manner by extruding aflowable material. The flowable material may be extruded through anextrusion tip carried by a print head of the system, and is deposited asa sequence of beads or layers on a substrate in an x-y plane. Theextruded flowable material may fuse to previously deposited material,and may solidify upon a drop in temperature. The position of the printhead relative to the substrate is then incrementally advanced along az-axis (perpendicular to the x-y plane), and the process is thenrepeated to form a 3D part resembling the digital representation.

Machine 1 includes a bed 20 provided with a pair of transversely spacedside walls 21 and 22, a gantry 23 supported on side walls 21 and 22,carriage 24 mounted on gantry 23, a carrier 25 mounted on carriage 24,an extruder 60, and an applicator assembly 26 mounted on carrier 25.Supported on bed 20 between side walls 21 and 22 is a worktable 27provided with a support surface disposed in an x-y plane, which may befixed or displaceable along an x-axis. In the displaceable version, theworktable 27 may be displaceable along a set of rails mounted on the bed20 by means of servomotors and rails 28 and 29 mounted on the bed 20 andoperatively connected to the worktable 27. Gantry 23 is disposed along ay-axis, supported at the ends thereof on end walls 21 and 22, eitherfixedly or displaceably along an x-axis on a set of guide rails 28 and29 provided on the upper ends of side walls 21 and 22. In thedisplaceable version, the gantry 23 may be displaceable by a set ofservomotors mounted on the gantry 23 and operatively connected to tracksprovided on the side walls 21 and 22 of the bed 20. Carriage 24 issupported on gantry 23 and is provided with a support member 30 mountedon and displaceable along one or more guide rails 31, 32 and 33 providedon the gantry 23. Carriage 24 may be displaceable along a y-axis on oneor more guide rails 31, 32 and 33 by a servomotor mounted on the gantry23 and operatively connected to support member 30. Carrier 25 is mountedon a set of spaced, vertically disposed guide rails 34 and 35 supportedon the carriage 24 for displacement of the carrier 25 relative tocarriage 24 along a z-axis. Carrier 25 may be displaceable along thez-axis by a servomotor mounted on carriage 24 and operatively connectedto carrier 25.

FIG. 1A shows a machine 1A, which may be a programmable computer numericcontrol (CNC) machine embodying aspects of the present disclosure.Features of machine 1A that correspond to features of machine 1 areindicated with the same numerals and may be provided in the same mannerdescribed above with respect to machine 1. Machine 1A may include acarrier 25A that operates in a manner similar to carrier 25.

As best shown in FIG. 2, carrier 25 is provided with a base platform 36,a gear box 37 fixedly mounted on the upper side thereof, and a mountingplatform 38 rotatably mounted on the underside of base platform 36.Fixedly mounted to the case of gearbox 37 is a positive displacementgear pump 74, driven by a servomotor 75, through a gearbox 76. Gear pump74 receives molten plastic from extruder 60, shown in FIG. 1, through aninput port 77, shown in FIG. 2. Platform 38 may be provided withopenings therethrough disposed along the z-axis of the carrier 25. Gearbox 37 may be provided with a gear arrangement having an openingtherethrough and disposed coaxially with the aligned openings in gearbox 37 and platforms 36 and 38, operatively connected to platform 38 forrotation about the z-axis and rotatable about such axis by means of aservomotor 39 mounted on base platform 36 and operatively connected tosuch gear arrangement. Applicator assembly 26 may include an uppersegment 41 and a lower segment 42. Upper segment 41 includes atransverse portion 41 a secured to the underside of mounting platform 38for rotational movement about the z-axis. Upper segment 41 may beprovided with an opening therethrough along such z-axis, and a dependingportion 41 b may be disposed substantially parallel relative to suchz-axis. Lower segment 42 includes a housing 42 b disposed on an innerside of depending portion 41 b. Housing 42 b may be mounted on a shaftjournalled in a lower end of depending portion 41 b, intersecting anddisposed perpendicular to the z-axis of carrier 25, and further housing42 b may be provided with a laterally projecting applicator head 43 at afree end thereof. Mounted on a gearbox 44 provided on an outer side ofdepending portion 41 b (opposite housing 42 b) is a servomotor 45operatively connected through gearbox 44 to the shaft journalled independing portion 41 b. Servomotor 45 may be configured for pivotallydisplacing lower segment 42 in a y-z plane. A material tamping roller 59(shown in FIG. 3), rotatably mounted in carrier bracket 47, provides ameans for flattening and leveling a bead of flowable material (e.g.,molten thermoplastic), as shown in FIG. 3. Carrier bracket 47 may beadapted to be rotationally displaced by means of a servomotor 60 (shownin FIG. 2), through a sprocket 56 and drive-chain 65 arrangement.

As shown in FIG. 2A, machine 1A may include a carrier 25A provided witha positive displacement gear pump 66, driven by a servomotor 67 througha gearbox 68. Gear pump 66 may receive molten plastic from extruder 60,as shown in FIG. 1A. Material may be pushed out of gear pump 66 to anapplicator head 43A. The material may proceed from gear pump 66 andthrough nozzle 51 to a substrate such as a surface of worktable 27 infront of material tamping roller 59. Roller 59 may be rotatably mountedin carrier bracket 47, and may provide a means for flattening andleveling a bead of flowable material as shown in FIG. 3A, for example.Carrier bracket 47 may be adapted to be rotationally displaced by meansof a servomotor 60, through a sprocket or gear 56 and a drive chain orbelt 65.

With reference to FIG. 3, applicator head 43 of machine 1 may include ahousing 46 with a roller bearing 49 mounted therein. Carrier bracket 47is fixedly mounted to an adaptor sleeve 50, journalled in bearing 49. Asbest shown in FIGS. 2-3, a conduit 52 including an elongated, flexiblematerial for conveying, e.g., a molten bead of a flowable material(e.g., molten thermoplastic) under pressure from a source (e.g., one ormore extruder 60 and an associated polymer or gear pump) disposed oncarrier 25, to applicator head 43, may be fixedly (or removably)connected to, and in communication with nozzle 51. An intermediateportion of conduit 52 may be routed through the openings through gearbox 37, base platform 36 and mounting platform 38, and along the z-axisof carrier 25. In use, the flowable material 53 (e.g., meltedthermoplastic) may be heated sufficiently to form a molten bead thereof,which is then forced through conduit 52 and delivered through applicatornozzle 51, to form multiple rows of deposited material 53 in the form ofmolten beads, as described herein. Such beads of molten material 53 maybe flattened, leveled, and/or fused to adjoining layers by any suitablemeans, such as, e.g., bead-shaping roller 59, to form an article. Eventhough bead-shaping roller 59 is depicted as being integral withapplicator head 43, bead-shaping roller 50 may be separate and discretefrom applicator head 43. In some embodiments, the deposited material 53may be provided with a suitable reinforcing material, such as, e.g.,fibers that facilitate and enhance the fusion of adjacent layers ofextruded flowable material 53.

With reference to FIG. 3A, applicator head 43A of machine 1A may includea housing 46 with a roller bearings 49 mounted therein. A conduit 52 forconveying a molten bead of flowable material under pressure from one ormore of extruder 60 and gear pump 66 to applicator head 43A may befixedly (or removably) connected to, and in communication with, a nozzle51. Thus, applicator head 43A may operate in a manner similar toapplicator head 43 of machine 1.

In some embodiments, machines 1 and 1A may include a velocimetryassembly (or multiple velocimetry assemblies) configured to determineflow rates (e.g., velocities and/or volumetric flow rates) of material53 being delivered from applicator heads 43 and 43A. The velocimetryassembly preferably transmits signals relating to the determined flowrates to the aforementioned controller coupled to machine 1, which maythen utilize the received information to compensate for variations inthe material flow rates.

In the course of fabricating a component, pursuant to the methodsdescribed herein, the control system of the machine 1, in executing theinputted program, may control the several servomotors described above todisplace the gantry 23 along the x-axis, displace the carriage 24 alongthe y-axis, displace the carrier 25 along a z-axis, pivot lowerapplicator segment 42 about an axis disposed in an x-y plane and rotatebracket 47 about a z-axis thereof, in accordance with the inputtedprogram, to appropriately deliver material 53 and provide the desiredend product or a near duplicate thereof. The control system of machine1A may control the several servomotors to display gantry 23, carriage24, and carrier 25A in a similar manner to appropriate deliver material53.

With reference now to FIG. 4, there is illustrated, a cross-sectionalschematic representation of a thermoplastic extrusion and applicationsystem, along with a block diagram of an exemplary servo controlcircuit, according to aspects of the present disclosure. FIG. 4 depictsan extruder 60, comprising a heavy duty screw 63, rotatably mountedinside a barrel 64, and driven by a servomotor 61 through a gearbox 62.One or both of the screw 63 and barrel 64 may be made of steel. Pelletsof material may be introduced into barrel 64 from a hopper 73. Those ofordinary skill will recognize that the pellets may be of any suitablematerial. For example, in one embodiment, pellets may be made ofthermoplastic material. In addition to pellets, the material may bedelivered to hopper 73 in any suitable size or configuration. Thepellets introduced into barrel 64 may be heated by the frictiongenerated from the rotation of screw 63 and/or one or more barrelheaters 65 disposed alone a length of barrel 64. Once the pellets havemelted, the molten material may be forced under pressure by screw 63,into a servo-controlled gear pump 66, driven by a servomotor 67, througha gearbox 68. Subsequently, the molten material is delivered from anoutlet of gear pump 66 to conduit 52 (FIGS. 2, 2A, 3, 3A) for use in 3Dprinting activities, as described above.

A stable flow rate into conduit 52 and through application nozzle 51 maybe regulated by providing servo control of the speed of gear pump 66,through an exemplary controller formed by the machine's control computer81 and servo control system, based on the speed of the CNC machine'smoving axes. The speed of extruder screw 63 likewise may be regulated inproportion with the speed of gear pump 66 by a servo control loop. Asignal from the gear pump servo loop is processed to control the outputof the extruder servo drive in proportion with that of gear pump 66,thus synchronizing the speed of the extruder with that of the gear pumpby a predetermined proportion. In other words, the operation speed ofgear pump 66 and extruder screw 63 may be dependent on one another. Thatis, the speed of extruder screw 63 may be determined as a function ofthe speed of gear pump 66, and vice versa. The speed of extruder screw63 also may be modified by inputs from one or more sensors 72 (e.g., apressure sensor or a flow sensor) operably coupled to the extruder.

As the feed rate of the CNC machine changes, representative servofeedback signals from the moving axes are processed in the machinecontrol computer 81 to control the speed of output pump 66, andcorrespondingly, the speed of extruder screw 63. Stated differently,machine control computer 81 serves to increase and/or decrease thespeeds of extruder screw 63 and gear pump 66 based onincreases/decreases in movement of CNC machine 1 during a 3D printingmanufacturing process. In embodiments where sensor 72 is a pressuresensor, sensor 72 may monitor the pressure at the inlet of gear pump 66,outputting an analog signal into servo controller 79 and/or machinecontrol computer 81, which in turn, influences the servo loopcontrolling the extruder screw 63 to bias, adjust, or otherwise finetune the synchronized speed between extruder screw 63 and gear pump 66,in order to compensate for pressure changes at the inlet of gear pump66. That is, changes in pressure at the inlet of gear pump 66 mayfurther be used to modify the speeds of extruder screw 63 and/or gearpump 66 and the relative speeds thereof. By coordinating the speed ofthe gear pump 66 with the speed of the extruder screw 63, whilecompensating for pressure variations, a constant output proportional tothe feed rate of the CNC machine may be achieved at the output of gearpump 66, and through application nozzle 51. With this approach, inputpressure is relatively constant because the extruder screw 63 and gearpump 66 change speeds at the same time, with minor adjustments beingmade to compensate for variables resulting from melt-temperature andpressure variations. Thus, the dimensions of a deposited bead ofmaterial remains relatively consistent and dimensionally stablethroughout the application process.

FIG. 4A illustrates a cross-sectional schematic representation of athermoplastic extrusion and application system, along with a blockdiagram of an exemplary servo control circuit. Extruder 60 may be drivenby servomotor 61 through gearbox 62, as discussed above with respect tomachine 1 and FIG. 4. A stable flow rate to conduit 52 and throughnozzle 51 may similarly be regulated by providing servo control of thespeed of gear pump 66, through an exemplary controller formed by thecontrol computer 81 and servo control system, based on the speed of themoving axes of machine 1A. Thus, machine 1A may be configured to providea consistent and dimensionally stable bead of material in a mannerdescribed above with respect to machine 1.

In addition to providing a consistent and dimensionally stable bead ofmaterial, CNC machines 1, 1A may also include a gear pump control switch80 that provides a user the ability to modify a size of the depositedbead of material. Control switch 80 may be a hardware switch connectedto machine control computer 81 and may control a speed (e.g.,revolutions per minute) of gear pump 66, for example. By manipulating(e.g., rotating) control switch 80, an operator may cause machinecontrol computer 81 to increase or decrease the size of the depositedbead, as described below. After this manipulation, the modified size maybe deposited in a consistent and dimensionally stable manner. Controlswitch 80 may be a knob, button(s), lever, or other physical switch.When physical, control switch 80 may be provided on a cabinet of machinecontrol computer 81, or may be provided at a location separate frommachine control computer 81. Control switch 80 may also be implementedas a “soft” switch (e.g., a switch, button, lever, or other feature)displayed on a touch-screen that may be operated by a user.

The ability to achieve a target pressure at an input of the melt pump bycontrolling the relative speeds of the extruder and gears of gear pump66 may also create the ability to further refine a CNC machine such asCNC machine 1A, improving throughput while generating a properly mixedand thermally homogenized melt. For example, in an exemplaryconfiguration shown in FIG. 4A, the target pressure may be achievedwithout the need to include a breaker plate or a screen. In one aspect,this may be achieved by control of gear pump 66 by a controller such asmachine control computer 81, which may output commands to servocontroller 79 and/or servo drive output 78. While the machine controlcomputer 81, servo controller 79, and servo drive output 78 may beprovided separately, one or more of these components may be combined. Inone aspect, machine control computer 81 may form a single control deviceor controller that includes one or more servo controllers 79 forreceiving feedback from servomotor 61 and servomotor 67, and one or moreservo drive outputs 78 that generate signals to drive servomotors 61 and67.

CNC machines 1, 1A may be configured to generate and maintain acontrolled target pressure at the input end of the gear pump 66. As theinput end of the gear pump 66 may also be an exit end of the extruder60, it may not be necessary to install a breaker plate or screen at theexit of the extruder to generate the pressure required for proper mixingin the extruder. The pressure at the inlet end of gear pump 66 may bedetermined or measured by one or more sensors 72, which may include apressure sensor as described above. As shown in FIG. 4A, an outlet endof the extruder 60 may also form an inlet end of the gear pump 66. Thus,sensor 72 may include a single pressure sensor that is configured tosense both a pressure of the inlet of gear pump 66 and a pressure of theoutlet of the extruder 60.

In an exemplary embodiment, the CNC machines 1, 1A may generate therequired pressure by controlling gear pump 66 via machine controlcomputer 81. Machine control computer 81 may be configured (e.g.,programmed with software) to allow a target pressure to be adjusted.Thus, extruder 60 and gear pump 66 may be able to accommodate differentrequirements that may be necessary for different materials (e.g.,different polymers). In one aspect, machine control computer 81 maycontrol extruder 60 and gear pump 66 to generate required pressureand/or adjust the pressure for a plurality of different polymers orflowable materials. For example, target pressures for a correspondingplurality of thermoplastic materials may be stored in a memory ofmachine control computer 81. Thus, when a first material having a firsttarget pressure is extruded, machine control computer 81 may control therelative speeds of extruder 60 (e.g., screw 63) and gear pump 66 toreach and maintain this target pressure. When the extruded materialchanges to a second material, machine control computer 81 may changethese relative speeds to reach and maintain a second target pressure,allowing the CNC machines 1, 1A to extrude multiple materials atdifferent respective pressures. In one example, changing the relativespeeds of the gear pump 66 and the extruder 60 may be performed bymaintaining the speed of the extruder 60 constant while changing thespeed of gear pump 66, or instead by maintaining the speed of gear pump66 constant while changing the speed of extruder 60. The relative speedsmay also be changed by modifying both of these speeds by differingamounts.

The ability to generate the required pressure may be accomplished with alower-cost system that reduces mechanical complexity without the needfor a breaker plate or a screen (such as a filter) between an end of thescrew 63 and gear pump 66, as shown in FIG. 4A, for example. Control ofgear pump 66 may be performed without unduly restricting throughput,resulting in higher flow rates for extruder 60.

In an exemplary configuration, nozzle 51 may have an open round shape(FIG. 6) which offers little resistance to material flow. Gear pump 66may restrict flow to the nozzle 51, thereby avoiding the need to providea nozzle having significant resistance to material flow. A desired oroptimal pressure within extruder 60 may be created and maintained bycontrolling the relative speeds of the extruder 60 and gear pump 66.

Melt pumps may be used in steady state plastic extrusion processing fortwo exemplary purposes. First, melt pumps may provide a way of assuringa steady flow of material which overcomes the tendency of extruders tovary the flow rate or “surge” over time. Second, melt pumps may increasethe pressure from the extruder to help force material through extrusiondies, which may have significant resistance to flow. Extruders may havea particular pressure range within which they operate optimally. If adie is provided and the pressure required to flow material through thedie is higher than the optimal range, a melt pump may be used generatethis higher pressure. However, by controlling flow with a gear pump(e.g., by restricting flow when necessary), the need for a breaker plateor a die may be eliminated. An optimal pressure within extruder 60 maybe maintained, while pressure may be varied in a controllable manner.Thus, a predetermined pressure which is based on the requirements of theparticular polymer material being extruded may be provided withoutchanging parts. The configuration may also generate a consistent,controllable flow rate to the print nozzle, resulting in a quality printprocess.

Controlling flow with a gear pump may also eliminate the need for amixing section, such as knobs, protrusions, or other shapes on thethreading of an extruder screw. Thus, each of the threads of an extruderscrew may present a uniform, even thread surface.

When additive manufacturing is performed to form a three-dimensionalobject, an example of which is shown in FIG. 5, several separate beads53 may be printed next to each other, to fuse with adjacent layers andform a solid one-piece object. Each of the two beads 53 may tend to formrounded edges. Thus, adjacent beads 53 disposed may tend to form a voidor hole 100 at positions below and above the rounded edges of the beads53. These holes 100 may be undesirable for three-dimensional objects,particularly for objects printed for use in an autoclave. In order toavoid the formation of holes 100, beads 53 may be deposited so as tooverlap by a certain amount.

With reference to FIG. 6, adjacent beads 53 may be deposited to have adesired overlap, which may be represented by a particular percent oramount. However, when a nozzle introduces this overlap while also movingby a constant amount throughout the print (e.g., when depositingparallel rows of beads), additional material may be squeezed out byroller 59, forming squeeze-out material 102. Squeeze-out material 102may result in an overlap between two beads by an unintended amount inaddition to the desired overlap. Squeeze-out material 102 may firstoccur with the third bead in a row of adjacent beads (resulting frommaterial squeezed out when the second bead 53 is applied so as tooverlap the first bead 53), and may become larger for each subsequentbead in an exponentially-increasing manner. Thus, the overlap mayquickly become significant, and may even result in one bead beingdeposited on another full bead of squeeze-out material 102, an outcomewhich would be very undesirable. For example, as shown in the top viewin FIG. 6, each bead may be deposited by a CNC machine 1 programmed fora constant amount or percent of desired (calculated) overlap 101.However, the actual amount the side of bead increases or squeezes out,may compound over time. As more beads 53 are printed, the squeeze-outmaterial 102 may grow accordingly.

One potential process to counteract the formation of squeeze-outmaterial 102 may employ a program that causes the nozzle 51 to move overthe distance including the desired overlap, plus an estimated amount ofsqueeze-out material 102, which may continue increasing. The nozzle 51would have to move over different distances when printing subsequentrows, which may make programming difficult.

In order to keep the amount (e.g., percentage) of overlap 101 constantfor each adjacent bead and keep the nozzle 51 moving over the sameconsistent amount for each row formed by a bead 53, the size (e.g.,width) of the third and any subsequent bead 53 may be reduced by aparticular (e.g., the same) amount to prevent squeeze-out material 102from building up. This reduction may be equal to a calculated amount ofsqueeze-out material 102 that would form if a size of the third bead isnot reduced. This reduction may be the same for the third bead 53 andfor each subsequent bead 53 adjacent to the third bead 53 in a directionperpendicular to a deposition direction.

In order to print the third bead 53 (and a subsequent bead 53) with areduced size, the print head may provide the ability to both: produce aconsistent-sized bead 53 at different machine speeds, and change thebead 53 to a smaller or larger sized bead as desired, while stillproducing the bead 53 with a consistent (changed) size. This may beperformed altering the relationship between the machine speed (e.g., atranslation speed of nozzle 51) and the melt pump speed. For example, aratio of the machine speed to the gear pump 66 speed may be altered.Such an alteration of the machine or nozzle translation speed to themelt pump speed may be performed by at least one of a CNC “G” codeprogram, or manually, by operating melt pump control switch 80. In oneaspect, the ratio of machine speed to nozzle translation speed may bechanged to a first value based on a program stored by machine controlcomputer 81, thereby adjusting the size of the bead 53 by a firstamount. The ratio of machine speed to nozzle translation speed may bechanged to a second value based on the operation of control switch 80,thereby adjusting the size of the bead 53 by a second amount. In oneaspect, machine control computer 81 may increase or decrease the size ofthe bead 53 by a first amount. Manipulation of melt pump control switch80 may increase or decrease the size of the bead 53 by a second amount.Thus, melt pump control switch 80 may be used to increase or decreasethe first amount.

The machine speed to melt pump speed relationship may be altered in theCNC program to cause an increase or decrease in bead 53 size by aparticular percentage. The bead 53 size can be increased or decreased bya lesser amount than the amount specified in the CNC program byoperating control switch 80. Thus, the control switch 80 may operateseparately from the adjustment in the program, allowing manualadjustment of the size of the bead 53.

For example, when first starting to print a three dimensional object,the bead 53 may differ by small amount than what was originallyspecified by the printing program. In one aspect, a slight operation ofthe control switch 80 may bring the bead 53 to the exact size that wasused to program the production of the three dimensional object.

In one aspect, by providing a program and/or control switch for changingbead size during printing, the formation of holes, which may be presentif the bead is smaller than what was specified in the printing program,may be avoided. Additionally, excessive squeeze-out, which may bepresent if every bead were produced larger than a size was specified inthe printing program, may also be avoided. Thus, a part may be printedin a precise manner.

As shown in FIG. 7, a plurality of beads 53 of flowable material may bedeposited in a manner that can form a boundary or fill area 104 (e.g., abounded area in which one or more beads 53 may be deposited to provide afill). By depositing one or more beads 53 in a closed path, a peripherymay be defined such that boundary or fill area 104 is located within theperiphery. When a boundary is formed, the boundary or fill area 104 mayresult in the formation of a void 103. In one aspect, control computer81 may determine when void 103 would be formed if bead width 53 isprovided with a value initially specified in a software (e.g., slicingsoftware) program.

In one aspect, machine control computer 81 may be programmed to evaluatethe boundary or fill area 104 and apply a standard size (e.g., width)for bead 53. A standard width may be specified by slicing software.Machine control computer 81 may determine when the area 104 can befilled without a void by using the standard width, and deposit beads 53accordingly.

In one aspect, control computer 81 may determine when void 103 would beformed if bead width 53 is provided with the standard width (e.g., avalue initially specified in a slicing software program). Machinecontrol computer 81 may be configured to determine when, by varying awidth of a plurality of beads 53 by a particular (e.g., the same)amount, a void 103 may be filled. This may include modifying a size of aplurality, or all, of the beads 53 within boundary or fill area 104.When control computer 81 (or a separate controller) determines that avoid 103 will be formed in area 104, as shown in FIG. 7, controlcomputer 81 may calculate a modified bead 53 size for a single bead thatwill completely fill void 103 in area 104. This modified bead 53 sizemay be larger or smaller than the standard bead size which was used todeposit adjacent beads 53. Thus, a size and/or shape of boundary or fillarea 104 (and a size or shape of one or more adjacent beads in boundaryor fill area 104) may be used to determine a speed of gear pump 66and/or a speed of translation of nozzle 51 that forms a plurality ofbeads 53 or a single bead 53 with an adjusted size to fill void 103.

In one aspect, the slicing software programmed in control computer 81may control the servo controller 79 to increase or decrease the machinespeed (e.g., translation speed of nozzle 51) to gear pump 66 speedrelationship by the amount (e.g., percentage) required to change thebead width to completely fill the boundary or fill area 104 as shown inFIG. 8. This may be performed to increase or decrease the size of asingle bead 53 or a plurality of beads 53.

While principles of the present disclosure are described herein withreference to illustrative embodiments for particular applications, itshould be understood that the disclosure is not limited thereto. Thosehaving ordinary skill in the art and access to the teachings providedherein will recognize additional modifications, applications,embodiments, and substitution of equivalents all fall within the scopeof the embodiments described herein. Accordingly, the inventionsdescribed herein are not to be considered as limited by the foregoingdescription.

We claim:
 1. A system for additive manufacturing, comprising: a nozzleconfigured to translate along a first axis, a second axis perpendicularto the first axis, and a third axis orthogonal to the first and secondaxes, wherein the nozzle is operably coupled to: an extruder having anoutlet and including a screw disposed within a barrel; and a pump havingan inlet and an outlet, the inlet being coupled to the extruder, and theoutlet being in fluid communication with the nozzle; and a controllerthat causes a speed of the pump with respect to a speed of the screw toadjust and thereby apply a target pressure at the outlet of theextruder, wherein the controller is programmed to change the targetpressure from a first target pressure stored in a memory of thecontroller to a second target pressure stored in the memory of thecontroller.
 2. The system of claim 1, further including a pressuresensor configured to sense a pressure of the inlet of the pump and apressure of an outlet of the extruder, the speed of the pump withrespect to the speed of the screw being adjusted based on the pressuresensed by the pressure sensor.
 3. The system of claim 1, wherein thepump is connected to the extruder without a breaker plate or a screendisposed between the pump and the extruder.
 4. The system of claim 1,wherein the outlet of the extruder and the inlet of the gear areprovided at a same location.
 5. The system of claim 1 wherein the changeto the second target pressure is performed based on a change of theflowable material.
 6. The system of claim 5, wherein the change inpressure to the second target pressure is performed based on pressurefeedback received by a pressure sensor.
 7. The system of claim 5,wherein the first target pressure is a pressure target associated with afirst flowable material and the second pressure target is a pressuretarget associated with a second flowable material, wherein the change tothe second target pressure is performed based on a determination by thecontroller that an extruded material has changed from the first flowablematerial to the second flowable material.
 8. The system of claim 1,wherein the controller is configured to adjust at least one of the speedof the pump or a translation speed of the nozzle based on a size of aboundary formed by at least one deposited bead of flowable material. 9.The system of claim 8, wherein the controller is configured to adjust atleast one of the speed of the pump or the translation speed of thenozzle based on a determination that a standard bead size will result inthe formation of a void.
 10. A system for additive manufacturing,comprising: a nozzle configured to translate along a first axis, asecond axis perpendicular to the first axis, and a third axis orthogonalto the first and second axes, wherein the nozzle is operably coupled to:an extruder including a screw disposed within a barrel; and a pumphaving an inlet and an outlet, wherein the inlet is coupled to theextruder, and the outlet is downstream of the extruder and in fluidcommunication with the nozzle; and a controller configured to modify asize of a bead extruded by the nozzle to maintain an approximatelyconstant sized overlap between a plurality of adjacent beads bymodifying a ratio of a translation speed of the nozzle and a speed ofrotation of the pump.
 11. The system of claim 10 wherein the ratio ischanged based on a program stored in the controller.
 12. The system ofclaim 10 further including a control switch, wherein the ratio ischanged based on an operation of the control switch.
 13. The system ofclaim 12, wherein the controller is configured to increase and decreasea speed of the gear pump based on the operation of the control switch.14. The system of claim 10 further including a control switch, whereinthe ratio is changed based on an operation of the control switch andbased on a program stored in the controller.
 15. The system of claim 14,wherein the controller is configured to change the ratio to a firstvalue based on the program stored in the controller, the controllerconfigured to further change the ratio to a second value based on theoperation of the control switch.
 16. The system of claim 10, wherein thecontroller is configured to change a size of a bead with respect to twoadjacent beads.
 17. The system of claim 10, wherein the controller isconfigured to adjust at least one of the speed of the pump or thetranslation speed of the nozzle based on a size of a boundary formed byat least one deposited bead of flowable material.
 18. The system ofclaim 17, wherein the controller is configured to adjust at least one ofthe translation speed of the nozzle based on a determination that astandard bead size will result in the formation of a void.
 19. Thesystem of claim 10, wherein the controller is programmed to change atarget pressure at an outlet of the extruder from a first targetpressure stored in a memory of the controller to a second targetpressure stored in the memory of the controller.
 20. The system of claim19, further including a pressure sensor configured to sense a pressureof the inlet of the pump and a pressure of an outlet of the extruder.